The broad, long-term objectives of this proposal are: (1) to elucidate the molecular basis of deafness in a large, recently identified, pedigree with cochlear deafness inherited by the interaction of a mitochondrial and autosomal mutation, (2) to apply what is learned from this specific case to the elucidation of the molecular basis of hearing and of inherited and acquired cochlear deafness in general, and (3) to design therapeutic approaches to prevent, correct, or circumvent those defects. The specific aims are an in-depth analysis of this pedigree at the clinical and molecular level: 1. Characterization of the clinical phenotype in greater detail. 2. Identification of the mitochondrial mutation responsible for deafness. 3. Demonstration that the autosomal locus is linked to a specific chromosomal region of the human genome. 4. Characterization of the functional effects of the mitochondrial mutation, and of its interactions with other cell constituents. The health-relatedness of the project is in its ability to provide prenatal diagnosis and possibly therapy for members of this pedigree, and to analyze other cases of inherited and acquired cochlear deafness for defects in the same genes or pathways involved in this family. The experimental design and methodology for the clinical portion involves structural and functional characterization of the auditory, vestibular, and other organ systems in clinically deaf individuals and their siblings, by clinical, laboratory, and imaging techniques. In addition, prospective examinations in infants at risk will be done to define the earliest changes in cochlear function. The experimental design and methodology for the laboratory portion will include identification of the mitochondrial mutation by enzymatic assays of oxidative phosphorylation, electrophoretic analysis of proteins, and DNA sequencing. Mapping of the autosomal mutation to a specific region of the human genome will involve a combination of linkage and candidate gene approaches. The functional effects of the mitochondrial mutation will be studied in culture cells using biochemical and molecular biological methods. The investigation of this unique pedigree provides an opportunity to dissect out the molecular basis of cochlear function and deafness. The insights gained raise the possibility of improved diagnostic, therapeutic, and preventive measures.